Electro-acoustic transducer and method of manufacturing transducer

ABSTRACT

An electro-acoustic transducer includes a tone generator, a vibrator, and a case. The tone generator includes a diaphragm, and a voice coil joined to the diaphragm. The vibrator includes a magnetic circuit having a magnetic gap at which the voice coil is positioned, and a suspension made of metal and having a first end joined to the magnetic circuit to suspend the magnetic circuit for allowing the magnetic circuit to vibrate. The case is joined to a periphery of the diaphragm, and includes a metal plate joined to a second end of the suspension. The metal plate is joined to the suspensions reliably, hence allowing the electro-acoustic transducer to be manufactured stably.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP03/012951.

TECHNICAL FIELD

The present invention relates to an electro-acoustic transducer used inportable communication devices, such as portable telephones, to generateringing tone and vibration for incoming calls, and a method ofmanufacturing the transducer.

BACKGROUND OF THE INVENTION

FIG. 4 is a cross-sectional view of a conventional electro-acoustictransducer disclosed in Japanese Patent Laid-Open Publication No.2000-153231. FIG. 5 is an enlarged cross-sectional view of thetransducer.

Diaphragm 1 is joined to frame 2 having a resin-molded periphery. An endof voice coil 3 is bonded to diaphragm 1. Upper plate 6 is bonded onmagnet 5 bonded on yoke 4. Magnetic circuit 7 includes yoke 4, magnet 5,and upper plate 6. The other end of voice coil 3 is positioned untouchedat magnetic gap 8 between yoke 4 and upper plate 6. Respective ends ofsuspensions 9 a and 9 b mounted on top and bottom surfaces of yoke 4,respectively are joined and suspended to frame 2. Suspension 9 a and 9 bare incorporated with resin caps 9 c provided at respective ends thereofby outsert molding. Resin caps 9 c are bonded to frame 2 and joinsuspensions 9 a and 9 b to frame 2. Yoke 4 and suspensions 9 a and 9 bare joined together by laser welding. Cover 2 a is joined to frame 2 andcovers an outer periphery of yoke 4.

An operation of the conventional electro-mechanical acoustic-transducerwill be described. A signal is input to voice coil 3. If a frequency ofthe input signal matches a mechanical resonance frequency of a vibratorcomposed of suspensions 9 a, 9 b and magnetic circuit 7, magneticcircuit 7 resonates and vibrates up and down intensely, thus causing auser of a portable communication device including the electro-acoustictransducer to feel the vibration. If the frequency of the input signalmatches a mechanical resonance frequency of a tone generator composed ofdiaphragm 1 and voice coil 3, diaphragm 1 resonates and vibrates up anddown intensely, causing the user of the portable communication device tonotice the vibration with sound.

The resonance frequency of magnetic circuit 7 may be set toapproximately 100 Hz, and the resonance frequency of the tone generatormay be set to approximately 1 kHz. The frequency of the input signal isselected, and the electro-acoustic transducer allows the user to feelthe vibration by contact and to notice the vibration by tone.

If the frequency of the input signal matches the resonance frequency ofmagnetic circuit 7, magnetic circuit 7 resonates and vibrates intensely.However, vibration of diaphragm 1 that is generated as a reaction of thevibration of magnetic circuit 7 does not have a frequency high enough toenable users to notice the vibration by sound.

If the frequency of the input signal matches a mechanical resonancefrequency of the tone generator composed of diaphragm 1 and voice coil3, diaphragm 1 resonates and vibrates intensely, enabling the user tonotice the vibration with sound. However, since magnetic circuit 7 doesnot follow the frequency of the input signal which is high due to alarge mass of magnetic circuit 7, the vibration of magnetic circuit 7that is generated as a reaction of the vibration of diaphragm 1 cannothave a large amplitude.

In the conventional electro-acoustic transducer, a surface of yoke 4 isprovided with Ni plating and Sn plating to secure enough joinitngstrength in vibrating components. Suspension 9 a and 9 b are welded tojoin to yoke 4 by laser beam. The production process, therefore, isunder complicated controls to restrain possible fluctuations of thejointing strength due to fluctuations of the thickness of the metalplating or intensity of the laser beam.

SUMMARY OF THE INVENTION

An electro-acoustic transducer includes a tone generator, a vibrator,and a case. The tone generator includes a diaphragm, and a voice coiljoined to the diaphragm. The vibrator includes a magnetic circuit havinga magnetic gap at which the voice coil is positioned, and a suspensionmade of metal and having a first end joined to the magnetic circuit tosuspend the magnetic circuit for allowing the magnetic circuit tovibrate. The case is joined to a periphery of the diaphragm, andincludes a metal plate joined to a second end of the suspension.

The metal plate is joined to the suspensions reliably, hence allowingthe electro-acoustic transducer to be manufactured stably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an electro-acoustic transduceracording to an exemplary embodiment of the present invention.

FIG. 2 is an exploded plan view of the electro-acoustic transduceraccording to the embodiment.

FIG. 3A is a cross-sectional view of the electro-acoustic transducer atline 3-3 in FIG. 2 according to the embodiment.

FIG. 3B is a cross-sectional view of another electro-acoustic transducerat line 3-3 in FIG. 2 according to the embodiment.

FIG. 4 is a cross-sectional view of a conventional electro-mechanicalacoustic transducer.

FIG. 5 is an exploded perspective view of the conventionalelectro-mechanical acoustic transducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a cross-sectional view of an electro-acoustic transduceraccording to an exemplary embodiment of the present invention. FIG. 2 isan exploded plan view of the electro-acoustic transducer. FIG. 3A is across-sectional view of the electro-acoustic transducer at line 3-3 inFIG. 2. Diaphragm 11 is joined to first case 12 a having a resin-moldedperiphery. An end of voice coil 13 is bonded to diaphragm 11. Plate 16is bonded on magnet 15 bonded on a yoke 14. Magnetic circuit 17 iscomposed of yoke 14, magnet 15 and plate 16. The other end of voice coil13 is positioned untouched at magnetic gap 18 between yoke 14 and plate16. Yoke 14 includes yoke body 14 a of magnetic materials and weight 14b having a large specific gravity on the periphery of yoke body 14 a.Weight 14 b is made of molded resin mixed with tungsten powder,provided. At the molding, an end of suspension 19 made of stainlesssteel sheet is incorporated in weight 14 b by outsert molding. Vibrator20 is composed of yoke 14 and suspension 19. The other end ofsuspensions 19 is welded on second case 12 b made of stainless steelsheet by YAG laser to suspend vibrator 20 movable up and down.

Case 12 b is mounted to case 12 a, thus providing the electro-acoustictransducer of the embodiment.

An operation of the electro-acoustic transducer of the embodiment willbe described.

A signal is input to voice coil 3. If the frequency of the input signalmatches a mechanical resonance frequency of the vibrator 20 composed ofsuspension 19 and magnetic circuit 17, magnetic circuit 17 vibrates upand down intensely. A user of a portable communication device includingthe electro-acoustic transducer feels the vibration (for example, at 130kHz) by contact. If the input signal has a voice frequency ranging aboutfrom 500 Hz to 10 kHz, diaphragm 11 vibrates back and forth, causing theuser to perceive the vibration by sound.

The resonance frequency of vibrator 20 including magnetic circuit 17 maybe set to approximately 100 Hz, and the resonance frequency of tonegenerator 21 may be set to approximately 1 kHz. Therefore, the frequencyof the input signal input to the electro-acoustic transducer isselected, and the user can perceive the vibration by contact or bysound.

If the frequency of the input signal matches the resonance frequency ofvibrator 20, magnetic circuit 17 resonates and vibrates back and forthintensely. However, the vibration of diaphragm 11 that is generated asreaction of the vibration of magnetic circuit 17 does not have afrequency high enough to notice the user of the vibration by sound.

If the frequency of the input signal matches the resonance frequency oftone generator 21 composed of diaphragm 11 and voice coil 13, diaphragm11 resonates and vibrates back and forth intensely, causing the user tonotice of the vibration by sound. The sound is typically used as aringing tone for incoming calls. However, since magnetic circuit 17cannot follow the frequency of the input signal, which is high, due to alarge mass of magnetic circuit 17, the vibration of magnetic circuit 17that is generated as reaction of the vibration of diaphragm 1 cannothave a large amplitude.

In the electro-acoustic transducer of the embodiment, tone generator 21has a resonance frequency of approximately 1 kHz, and the sound havingthe frequency is used as a ringing tone for incoming calls. Instead,when a melody is required for incoming calls, an input signal having afrequency corresponding to the melody is applied to voice coil 13, henceallowing diaphragm 11 to produce the melody. In this case, tonegenerator 21 may have is a flat frequency characteristic in an audiblefrequency range, for instance, from 500 Hz to 10 kHz, so that theresonant frequency is not emphasized.

A method of welding second case 12 b on suspension 19 with YAG laserwill be explained in detail. Case 12 b is provided with shoulder 12 c bydraw forming, as shown in FIG. 3A. The other end of suspension 19 ispositioned on flat portion 12 f of shoulder 12 c, and then, is weldedfrom above the suspension by the laser. Flat portion 12 f of shoulder 12c communicates with a side wall of second case 12 b via connection 12 g.If shoulder 12 c does not have an area enough for the welding as awelding region, shoulder 12 c may be further processed to be providedwith pedestal 12 e as the welding region by draw forming at leastadjacent only to suspension 19, as shown in FIG. 3B. This structureallows suspension 19 to be positioned on the welding region of shoulder12 c easily. The intensity of the laser may be determined so that a weldmark is visible from the backside surface, and the weld mark allows thewelding to be judged in acceptance or defect. The size and position ofpedestal 12 e formed by draw forming may be determined arbitrary. Thatis, the region enable for the welding may be determined easily.

Corner 12 d having a small radius of curvature may be adopted as afulcrum of suspension 19 vibrating. The corner stabilizes the back andforth vibration of the suspension as well as the vibrationcharacteristic, i.e., the resonance frequency of mechanical vibration.

The welding with YAG laser can limit a welded area and can reducethermal influence to adjacent areas. That is, the method is suitable forwelding small electronic components. Welding methods with laser otherthan the YAG laser also limit the region. Suspension 19 and second case12 b are made of stainless steel sheet. The intensity of the laser isdetermined so that a weld mark is visible from the backside surface. Theweld mark allows the welding to be judge in acceptance or defect, asdescribed above. The judging with the weld mark can be adopted also injudging weld quality of components made of metal sheet. The method ofjudging accomplishes a reliable welding for metal sheets used incomponents and to produce devices including the components without anytroublesomeness.

The corner of shoulder 12 c tends to have an inner wall having an arcshape. Corner 12 d preferably has an arc shape having a small radius ofcurvature. If the radius of curvature of corner 12 d changes by not lessthan 1.0 mm during back and forth movements of suspension 19, themechanical resonance frequency changes. This change prevents theposition of the welding region from being determined easily for providea predetermined resonance frequency.

The radius of curvature of corner 12 d preferably is not more than 1.0mm, and more preferably, is not more than 0.8 mm to provide a morestablevibration property. Corner 12 d of shoulder 12 c formed by the drawforming may not have a predetermined radius of curvature depending onmaterial of second case 12 b. In this case, a sheet made of materialincluded commonly in case 12 b and suspension 19 may be placed betweenshoulder 12 b and suspension 19 during the welding, thereby allowingcorner 12 d not to have the predetermined radius of curvature inshoulder 12 c.

The welding is carried out with YAG laser according to the embodiment.Laser other than the YAG laser, such as laser diode, may be employed tocarry out the welding as long as the weld mark is visible from the backside of the weld region.

The electro-acoustic transducer of the embodiment includes a single kindof suspension 19, but may include two kinds of suspensions havingdifferent heights joined to yoke 14 similarly to a conventionalelectro-acoustic transducer shown in FIG. 5. In this case, the two kindsof suspensions are joined to two shoulders having different heights,respectively.

INDUSTRIAL APPLICABILITY

An electro-acoustic transducer according to the present inventionincludes a suspension and a case made of metal sheet. The suspension andthe case are joined stably, thus allowing transducer to be manufacturedat a high productivity.

1. An electro-acoustic transducer comprising: a tone generator includinga diaphragm, and a voice coil joined to the diaphragm; a vibratorincluding a magnetic circuit having a magnetic gap at which the voicecoil is positioned, a suspension made of metal and having a first endjoined to the magnetic circuit to suspend the magnetic circuit forallowing the magnetic circuit to vibrate; and a case joined to aperiphery of the diaphragm, the case including a metal plate joined to asecond end of the suspension; wherein the case includes a first casejoined to the periphery of the diaphragm, and a second case mounted tothe first case and having the metal plate, wherein the second end of thesuspension and the metal plate are joined together by laser welding,wherein the metal plate of the case includes a shoulder facing inside ofthe case, wherein the second end of the suspension is joined to theshoulder, and wherein the shoulder has a corner closer to an inside ofthe case than a position at which the second end of the suspension isjoined to the shoulder, the corner of the shoulder having a radius ofcurvature.
 2. The electro-acoustic transducer of claim 1, wherein theshoulder includes a flat portion parallel to the suspension, beingjoined to the suspension, and a joint joining the flat portion and thecase, the joint extending from a joined region of the flat portion atwhich the flat portion is joined to the suspension, the joint extendingin a direction in which the suspension extends, and wherein a cornerprovided between the flat portion and the joint having a radius ofcurvature less than 1.0 mm.
 3. The electro-acoustic transducer of claim1, wherein the shoulder includes a pedestal facing inside of the caseand joined to the second end of the suspension.
 4. A method ofmanufacturing an electro-acoustic transducer, said method comprising:joining a diaphragm and a voice coil; joining a magnetic circuit and afirst end of a suspension made of metal, the magnetic circuit having amagnetic gap; placing a shoulder of a metal plate of a case in directcontact with a second end of the suspension; welding the shoulder of themetal plate of the case to the second end of the suspension by radiatinglaser onto one of the shoulder of the metal plate and the second end ofthe suspension; observing a weld mark produced by said welding of themetal plate from other of the shoulder of the metal plate and the secondend of the suspension; quitting said welding of the metal plateaccording to a status of the observed weld mark; and joining the caseand the periphery of the diaphragm by positioning the voice coil in themagnetic gap.
 5. The method of claim 4, wherein the case includes afirst case and a second case including the metal plate, and wherein saidjoining of the case to the periphery of the diaphragm includes joiningthe first case to the periphery of the diaphragm, said method furthercomprising jointing the first case to the second case.
 6. Theelectro-acoustic transducer of claim 1, wherein the metal plate has afirst surface and a second surface opposite to the second surface, thefirst surface facing inside of the case, the second surface facingoutside of the case, the first surface of the metal plate being coupledto the suspension, said electro-acoustic transducer further comprising aweld mark produced by the welding, the weld mark being visible from thesecond surface of the metal plate.
 7. The method of claim 4, wherein theshoulder of the metal plate has a first surface and a second surfaceopposite to the first surface of the metal plate, said welding theshoulder of the metal plate comprises welding the second end of thesuspension to the first surface of the shoulder of the metal plate, andsaid observing the weld mark comprises observing the weld mark from thesecond surface of the shoulder of the metal plate.
 8. Theelectro-acoustic transducer of claim 1, wherein the shoulder is formedby draw forming.
 9. The method of claim 4, further comprising formingthe shoulder of the metal plate of the case by draw forming.